Plumbing for variations headers from synthetic field trials.

BUG=428055

Review URL: https://codereview.chromium.org/688973004

Cr-Commit-Position: refs/heads/master@{#302331}

2 files changed, 43 insertions, 0 deletions

diff --git a/components/metrics/metrics_service.cc b/components/metrics/metrics_service.cc
index 4db3bb5..4fa2e75 100644
--- a/components/metrics/metrics_service.cc
+++ b/components/metrics/metrics_service.cc
@@ -1138,6 +1138,18 @@ bool MetricsService::UmaMetricsProperlyShutdown() {
   return clean_shutdown_status_ == CLEANLY_SHUTDOWN;
 }
 
+void MetricsService::AddSyntheticTrialObserver(
+    SyntheticTrialObserver* observer) {
+  synthetic_trial_observer_list_.AddObserver(observer);
+  if (!synthetic_trial_groups_.empty())
+    observer->OnSyntheticTrialsChanged(synthetic_trial_groups_);
+}
+
+void MetricsService::RemoveSyntheticTrialObserver(
+    SyntheticTrialObserver* observer) {
+  synthetic_trial_observer_list_.RemoveObserver(observer);
+}
+
 void MetricsService::RegisterSyntheticFieldTrial(
     const SyntheticTrialGroup& trial) {
   for (size_t i = 0; i < synthetic_trial_groups_.size(); ++i) {
@@ -1145,6 +1157,7 @@ void MetricsService::RegisterSyntheticFieldTrial(
       if (synthetic_trial_groups_[i].id.group != trial.id.group) {
         synthetic_trial_groups_[i].id.group = trial.id.group;
         synthetic_trial_groups_[i].start_time = base::TimeTicks::Now();
+        NotifySyntheticTrialObservers();
       }
       return;
     }
@@ -1153,6 +1166,7 @@ void MetricsService::RegisterSyntheticFieldTrial(
   SyntheticTrialGroup trial_group = trial;
   trial_group.start_time = base::TimeTicks::Now();
   synthetic_trial_groups_.push_back(trial_group);
+  NotifySyntheticTrialObservers();
 }
 
 void MetricsService::RegisterMetricsProvider(
@@ -1166,6 +1180,11 @@ void MetricsService::CheckForClonedInstall(
   state_manager_->CheckForClonedInstall(task_runner);
 }
 
+void MetricsService::NotifySyntheticTrialObservers() {
+  FOR_EACH_OBSERVER(SyntheticTrialObserver, synthetic_trial_observer_list_,
+                    OnSyntheticTrialsChanged(synthetic_trial_groups_));
+}
+
 void MetricsService::GetCurrentSyntheticFieldTrials(
     std::vector<variations::ActiveGroupId>* synthetic_trials) {
   DCHECK(synthetic_trials);
diff --git a/components/metrics/metrics_service.h b/components/metrics/metrics_service.h
index eae44f3..19794ea 100644
--- a/components/metrics/metrics_service.h
+++ b/components/metrics/metrics_service.h
@@ -21,6 +21,7 @@
 #include "base/metrics/histogram_flattener.h"
 #include "base/metrics/histogram_snapshot_manager.h"
 #include "base/metrics/user_metrics.h"
+#include "base/observer_list.h"
 #include "base/time/time.h"
 #include "components/metrics/clean_exit_beacon.h"
 #include "components/metrics/metrics_log.h"
@@ -76,6 +77,17 @@ struct SyntheticTrialGroup {
   SyntheticTrialGroup(uint32 trial, uint32 group);
 };
 
+// Interface class to observe changes to synthetic trials in MetricsService.
+class SyntheticTrialObserver {
+ public:
+  // Called when the list of synthetic field trial groups has changed.
+  virtual void OnSyntheticTrialsChanged(
+      const std::vector<SyntheticTrialGroup>& groups) = 0;
+
+ protected:
+  virtual ~SyntheticTrialObserver() {}
+};
+
 // See metrics_service.cc for a detailed description.
 class MetricsService : public base::HistogramFlattener {
  public:
@@ -211,6 +223,12 @@ class MetricsService : public base::HistogramFlattener {
   // To use this method, SyntheticTrialGroup should friend your class.
   void RegisterSyntheticFieldTrial(const SyntheticTrialGroup& trial_group);
 
+  // Adds an observer to be notified when the synthetic trials list changes.
+  void AddSyntheticTrialObserver(SyntheticTrialObserver* observer);
+
+  // Removes an existing observer of synthetic trials list changes.
+  void RemoveSyntheticTrialObserver(SyntheticTrialObserver* observer);
+
   // Register the specified |provider| to provide additional metrics into the
   // UMA log. Should be called during MetricsService initialization only.
   void RegisterMetricsProvider(scoped_ptr<MetricsProvider> provider);
@@ -358,6 +376,9 @@ class MetricsService : public base::HistogramFlattener {
   // Sets the value of the specified path in prefs and schedules a save.
   void RecordBooleanPrefValue(const char* path, bool value);
 
+  // Notifies observers on a synthetic trial list change.
+  void NotifySyntheticTrialObservers();
+
   // Returns a list of synthetic field trials that were active for the entire
   // duration of the current log.
   void GetCurrentSyntheticFieldTrials(
@@ -447,6 +468,9 @@ class MetricsService : public base::HistogramFlattener {
   // Field trial groups that map to Chrome configuration states.
   SyntheticTrialGroups synthetic_trial_groups_;
 
+  // List of observers of |synthetic_trial_groups_| changes.
+  ObserverList<SyntheticTrialObserver> synthetic_trial_observer_list_;
+
   // Execution phase the browser is in.
   static ExecutionPhase execution_phase_;